An aneurysm is an abnormal local dilation of an artery caused by a weakening of the artery wall. In the past, cerebral aneurysms were frequently treated by direct surgical intervention. For example, by installing a clip around the base of the aneurysm to prevent passage of blood between the aneurysm and the lumen of the vessel. Attempts have then been made to develop minimally invasive techniques for treating such aneurysms, for example, by filling the aneurysm with coils, such that the aneurysm eventually becomes a solid mass of coils and thrombus.